javascript 添加由另一个变量组成的变量时获取 NaN
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Getting NaN when adding variables which consists of another variables
提问by Jay
var dml = 30
var dd = parseFloat(document.getElementById("DriverD").value) <----- Only numbers like 10
var dm = dd-dml
alert((dd - dml) * 0.75) <----- This works
alert(dm * 0.75) <----- This returns NaN
alert(typeof(dm)) <----- This show that dm is a Number
I'm not sure why I keep getting NaN. I already tried parseFloatand parseIntbut still showing NaN when multiplying a variable (dm) which consists of variables (dd-dml). dm is the result of subtracting dml with dd or 10-30. Please share your solutions.
我不确定为什么我一直收到 NaN。我已经尝试过parseFloat，parseInt但在乘以由变量 (dd-dml) 组成的变量 (dm) 时仍然显示 NaN。dm 是用 dd 或 10-30 减去 dml 的结果。请分享您的解决方案。
I'm new here and I need help, please don't troll :) I am trying to add a cost calculator to my website.
我是新来的，我需要帮助，请不要巨魔:) 我正在尝试向我的网站添加成本计算器。
回答by smttsp
It seems fine to me.
对我来说似乎很好。
I want to tell another possible problem: You dont check if document.getElementById("DriverD").valueis a number or not. If a user enters a string or other type, it will cause a problem.
我想告诉另一个可能的问题：你不检查是否document.getElementById("DriverD").value是一个数字。如果用户输入字符串或其他类型，则会导致问题。
回答by PointedEars
The only reason you could get NaNhere is that the value of ddis NaN. Because the value of dmis defined as dd - dmland the value of dmlis a Numbervalue, 30.
你能得到的唯一原因，NaN这里要说的是价值dd为NaN。因为 的值dm被定义为dd - dml并且 的值dml是一个Number值，30。
parseFloat()always returns a Numbervalue. The -operator converts its operands to Numberonly if necessary. So the value of dmmust by definition be a Numbervalue.
parseFloat()总是返回一个Number值。该-操作其操作数转换为Number在必要时只。因此，dm根据定义，值必须是一个Number值。
However, NaNis a Numbervalue (typeof NaN === "number"), and it is "toxic": once an operand is NaN, the result of all following arithmetic operations is NaN.
然而，NaN是一个Number值 ( typeof NaN === "number")，它是“有毒的”：一旦一个操作数是NaN，其后所有算术运算的结果就是NaN。
That means that parseFloat()must have returned NaN, which means that the argument to parseFloat()could not be interpreted as the prefix of a decimal number representation.
这意味着parseFloat()必须返回NaN，这意味着parseFloat()无法将参数解释为十进制数字表示的前缀。
One common reason for that is that the user has typed thousands separators (which are not supported) or a decimal comma while only a decimal point is supported.
一个常见的原因是用户输入了千位分隔符（不支持）或十进制逗号，而只支持小数点。
回答by iftkhar
Trythis one
试试这个
var dml = 30;
var dd = parseFloat(document.getElementById("DriverD").value) ; <----- Only numbers like 10
var dm=0;
dm = dd-dml;
alert((dd - dml) * 0.75); <----- This works
alert(dm * 0.75); <----- This returns NaN
alert(typeof(dm)); <----- This show that dm is a Number
回答by Sebastian Korszon
I am a newbie but I think it is the type error, solution:
我是新手，但我认为是类型错误，解决方法：
var someV = parseInt(document.getElementById("some-v-id").value, 10) || 0,
parseInt(value, 10) - you know because you used parse float, but two pipes and zero might prevent you from NaN as JavaSrcipt might be treating 0 as a string.
parseInt(value, 10) - 您知道，因为您使用了解析浮点数，但是两个管道和零可能会阻止您使用 NaN，因为 JavaSrcipt 可能会将 0 视为字符串。
回答by Asish AP
Try this
试试这个
Two operands must be convert to parseFloat
两个操作数必须转换为 parseFloat
<input type="text:" value="10" id="DriverD" />
var dml = parseFloat(30);
var dd = parseFloat(document.getElementById("DriverD").value);
var dm = dd-dml;
alert(dm * .10);
Result is -.2
结果是 -.2
